A pile of x86 fixes:
- Prevent a memory leak in ioperm which was caused by the stupid
assumption that the exit cleanup is always called for current, which is
not the case when fork fails after taking a reference on the ioperm
bitmap.
- Fix an arithmething overflow in the DMA code on 32bit systems
- Fill gaps in the xstate copy with defaults instead of leaving them
uninitialized
- Revert: o"Make __X32_SYSCALL_BIT be unsigned long" as it turned out
that existing user space fails to build.